Diesel engines are used to provide power in a variety of applications, such as vehicle and work machine propulsion and a variety of other industrial applications. In some of these applications, the diesel engine may be required to remain on and idling with a light load or no load, and then be able to instantaneously apply full power at cutover to driving a load. In one example, a diesel engine may be a backup power source for a device such as a generator, with the backup engine being engaged to drive the device if the primary power source fails. In applications such as backing up hospital generators, it may be critical for the backup engine to transition to driving the generator immediately so that transmission of electricity to critical equipment and systems of the hospital is not interrupted.
To ensure that the diesel engine can provide the necessary power at cutover to driving a load, a higher fuel flow rate must be maintained than is required to operate the engine at the idle speed. Additionally, other systems may require greater energy output by the idling engine in order to handle the load, such as turbochargers that require higher exhaust manifold energy to drive the turbocharger and provide boost pressure to the engine so the engine does not have to use energy to suck air into the manifold. Methods exist for increasing the fuel flow rate and producing extra exhaust energy to spool up a turbocharger when the engine is on standby and would be idling. In one method, an actual parasitic load is applied to the backup engine. An oil pump or another generator can be hooked up to waste energy back into a cooling system or other system that can dissipate the energy. The parasitic load makes the engine governor think that the generator or other work load is engaged, and the governor reacts by increasing the fuel flow rate to maintain the engine speed. The parasitic load is removed when the backup engine cuts over to the generator load, and the backup engine is already operating with the necessary fuel flow rate and the turbocharger spooled up to drive the generator.
As an alternative to an actual parasitic load, the backup engine can be tricked into increasing the fuel flow rate and exhaust energy output by applying a virtual parasitic load. One strategy for creating a virtual parasitic load involves releasing exhaust energy from the engine cylinders during the expansion stroke before all the combustion energy is transferred to the crankshaft. A small fuel burn is allowed to occur before opening the exhaust valve to keep the engine turning, but much of the energy is dissipated. At low fuel flow rates such as fuel flows that should cause the engine to run at the idle speed, insufficient energy is created during the partial fuel burn to achieve the idle speed. The engine governor responds in a similar manner as when an actual load is applied by increasing the fuel flow rate until the engine gets up to the idle speed. At the same time, the excess exhaust energy will spool up the turbocharger so the fuel flow rate and the intake manifold pressure are at the levels required for a smooth transition during the transient response to cutover to driving the generator.
Early Exhaust Valve Opening (EEVO) for creating virtual parasitic loads as described above can be an effective solution to increasing fuel flow rates, intake manifold pressures and exhaust temperatures without increasing the engine power output. U.S. Pat. No. 5,937,807 issued to Peters et al. on Aug. 17, 1999, entitled “Early Exhaust Valve Opening Control System and Method,” discloses an exhaust valve system for an internal combustion engine including a turbocharger for effectively increasing the turbocharged boost pressure at low load engine conditions to improve engine transient response. The exhaust valve system includes an advanced timing mode for advancing the timing of the opening of the exhaust valve to an advanced opening crank angle prior to the normal opening crank angle while maintaining the timing of normal closing of the exhaust valves at a normal closing crank angle. The exhaust valve control device includes a dedicated advanced timing mode rocker lever capable of selectively actuating one of a pair of exhaust valves to create an early opening exhaust event prior to a normal exhaust event. An advanced cam lobe on the camshaft has a cam profile shape capable of the advanced timing mode rocker lever to pivot through an early opening exhaust valve stroke prior to the normal exhaust valve event.
U.S. Pat. No. 9,234,467 issued to Ernest et al. on Jan. 12, 2016, entitled “Engine System and Operation Method Using Engine Braking Mechanisms for Early Exhaust Valve Opening,” discloses a valve actuation system for an internal combustion engine that includes one or more first cams having a compression-release lobe and a main exhaust lobe adapted to transfer valve actuation motion to a first set of exhaust valves, and one or more second cams having an EEVO lobe and a main exhaust lobe adapted to transfer valve actuation motion to a second set of exhaust valves. The valve actuation system may provide any combination of main exhaust valve actuation with or without compression release actuation with main exhaust valve actuation with or without EEVO for the two sets of cylinders. Compression release or compression braking uses the engine to absorb power and provide a retarding force to slow a vehicle or machine in situations such as when the vehicle or machine is traveling downhill. To achieve compression braking, fuel flow to the engine is cutoff and the engine is turned into an air compressor driven by the machine's momentum. The intake and exhaust valves are generally operated as normal, and air is compressed in the engine cylinders during the compression stroke. The valve actuation system of Ernest et al. either provides an additional compression release lobe on the exhaust cam, or an additional cam with a compression release lobe, to open the exhaust valves when the cylinders reach top dead center of the compression strokes to blow the compressed air into the exhaust system instead of transferring power to the crankshaft. In both the Peters et al. and the Ernest et al. systems, early exhaust valve opening for EEVO events and/or compression braking is accomplished by modifying the exhaust valve cams or providing additional exhaust valve cams.